103 



sheltered retreats in which to lurk or to get away from the hot dry sum- 

 mers aud the long cold winters. 



In the third place, the comparative aridity of the region where these 

 claims are located renders the growth of them somewhat slower than 

 where the precipitation is more bountiful. This slowness of growth, 

 while it is an advantage in oue respect, aids the insect foes to a con- 

 derable extent in their work of destruction. A rank and rapid growth 

 places a tree out of danger from external enemies much more quickly 

 than will a slow growth. At the same time in rank growth a much 

 greater amount of food is furnished for the same number of insects, 

 and as a consequence less injury to the tree results than would were 

 the growth slower. 



A fourth cause for the rapid increase among these different insects 

 in new regions is the absence of such fungoid diseases as are known to 

 attack and kill various of these pests. After awhile, however, the 

 germs of these diseases become diffused through the soil, vegetable 

 debris, and about the encumbering growths, buildings, etc. These 

 germs are carried around by the elements and other agencies, and in 

 time some of them find lodgment within the bodies of such insects as 

 are susceptible to their growth. The result is disease and death. 



Comparative Freedom of different Trees from the Attacks of Insect Pests. — 

 Up to the present writing I have not sufficiently investigated this por- 

 tion of the subject to be entirely positive in my assertions as to the 

 kind or kinds of trees most nearly exempt from the attacks of insect 

 foes in different regions. None of them are entirely free ; but that there 

 are trees which suffer less than others in this respect is a well-known 

 fact, and can be seen at any time where several kinds are growing side 

 by side or in the same grove. Again, a particular kind of tree might 

 be troubled in a given locality, while in another it would be compara- 

 tively free. Some trees also suffer while small, and others are usually 

 injured after they have gained considerable growth and age. These 

 variations with regard to insect attacks among different trees, and of 

 the same kind at different ages, are governed by laws the explanation 

 of which would require much more time and space than I have at my 

 command. By looking over the list of insects mentioned above it will 

 be seen that no reference is made of any species injuring either the 

 Catalpa or Russian Mulberry. The Ash is affected by three, each of 

 which at times strips it of foliage while young; the Box Elder by two 

 or three ; the Willow by a dozen or more ; the Cottonwood by four or 

 five; the Soft-Maple by several ; the Elm a couple ; the Honey Locust 

 two, etc. 



In treating this subject only such insects have been mentioned as 

 have been ascertained to attack the various trees during their first few 

 years of growth, and before they have attained any great size. Other 

 species of insects injure these trees later on ; but, as a rule, these latter 



